1. Field of the Invention
The present invention relates to a vehicle alternator.
2. Description of the Related Art
A vehicle alternator comprises a rotor having a pair of pole cores (Lundell-type pole cores), each comprising a plurality of claws. The rotor provided with high-speed rotation generates electricity. A magnet, which is magnetized in a direction to reduce a leakage of magnetic flux, is inserted between two neighboring claws of the pole cores.
In many cases, the magnet is contained in a holder (a case) and is inserted between two neighboring claws like a vehicle alternator disclosed, for example, in Japanese unexamined patent publication No. 2005-80472, in order to protect the magnet and to simplify assembly.
However, the holder disclosed in the above-mentioned Japanese unexamined patent publication allows a part of the magnet to be exposed, which can cause the magnet to get wet when the rotor gets wet The wet magnet accelerates corrosion of the magnet and can deteriorate the generation of electricity caused by decreased magnet flux. Further, if the magnet becomes cracked, the cracked pieces could fly out and can be trapped between the rotor and a stator, thereby locking the rotational movement of the rotor. Resolving these problems is beyond the capability of the conventional vehicle alternators.
On the other hand, the magnet included in the holder can rattle because of production tolerance variations. The rattling of the magnet can lead to breakage of the magnet and can generate noise.